Sample QPO from XTE J1550-564

Above: (left) This 40 second snippet of
data captured by the Rossi X-ray Timing Explorer shows how the
x-ray flux from XTE J1550 oscillates during a flare in 1998.
Numbers on the vertical axis represent the number of x-ray photons
per second in the 2 to ~30 keV energy band. (right)
The Fourier power spectrum of the same 40s time series shows
a dominant spike at 0.3 Hz, corresponding to a period of about
3 1/3 seconds. Although 0.3 Hz is dominant, the spectrum reveals
frequency components extending to 1 Hz and higher.